Microwave reheating of frozen meals provides convenience for people seeking quick meal solutions because of the rapid thermal energy transfer into the food materials by the microwaves. However, microwave heating of frozen food is, in general, perceived as difficult and has many problems associated with it, such as overcooking of some portions of meals, cold spots, burnt edges and sauce splatter. In many instances, the meal experiences serious burnt spots yet some places are still very cold, even often below 0° C. Furthermore, the concentration of the microwave energy on spots tends to create local boiling of the water contained in the food and/or sauce and therefore splattering off the dish. Many attempts have been made in the past to solve this issue of re-heating frozen food in a more effective way.
It has been proposed in U.S. Pat. No. 4,351,997 to provide a modified form of tray structure to attempt to provide a more even heating of foodstuff in the tray when exposed to microwave radiation. This prior art has a bottom wall of microwave-transparent material and an upwardly-extending peripheral wall that is outwardly curved at its upper end to define a horizontal peripheral rim. The rim is partly or completely coated with a material that is reflective and opaque to microwave radiation, such as aluminum foil. The peripheral wall also is partly or completely coated with the foil material. The effect of this aluminum foil coating on the wall is to provide reflection of microwave energy toward the center of the tray.
U.S. Pat. No. 4,626,641 describes an embodiment in which a similar structure is provided. In addition to the provision of aluminum foil in the side wall of a tray, the foil also extends into the base of the container but leaves a rectangular open area in the bottom wall.
U.S. Pat. No. 5,310,980 relates to a tray useful for the microwave cooking of prepared foodstuff that comprises an outer layer formed of paperboard or molded plastic to which is laminated an inner polymeric film layer. A layer of microwave-reflective material, usually aluminum foil, is positioned between the outer and inner layers in the location of the peripheral wall of the tray and in a pattern in a portion of the bottom wall.
JP 09-369450 relates to a container for a microwave oven that comprises a first microwave reflecting plate placed along a circumferential lateral parts and a second microwave reflecting plates in the base section of the container.
It is apparent from the prior art that attempts have essentially been made to provide energy transmission structures with reflective material placed in locations that enable energy transfer from the edges and corners of the plate to a more central area of the plate. However, experimental trials have shown that these structures are, by themselves, insufficient to overcome the problems of uneven heating. In particular, cold areas are still present in the food despite the presence of these structures. Thus, improvements in these devices are needed and are provided by the present invention.